1. Field of the Invention
The present invention relates to a method and apparatus for optimizing a relationship between fire energy and drop velocity in an imaging device, and, more particularly, in one embodiment, to a method and apparatus for adjusting pre-fire and fire pulses used to jet ink from a printhead in an imaging device.
2. Description of the Related Art
An ink jet printer typically includes a printhead, which is carried by a carrier. The printhead is fluidly coupled to an ink supply. Such a printhead includes a plurality of nozzles having corresponding ink ejection actuators, such as heater elements.
Ink is jetted from the nozzles onto a print medium at selected ink dot locations within an image area. The carrier moves the printhead across the print medium in a scan direction while the ink dots are jetted onto selected pixel locations within a given raster line. Between passes of the printhead, the print medium is advanced a predetermined distance and the printhead is again moved across the print medium.
Ink jet printers may utilize a single printhead, or multiple printheads. For example, some ink jet printing systems utilize a monochrome ink cartridge including a monochrome, e.g. black, printhead, and a color ink cartridge including a color printhead having cyan, magenta and yellow nozzle groups. In another type of ink jet printing system, each printhead is connected to a respective remote ink supply.
The manufacture of printheads involves certain manufacturing tolerances resulting in manufacturing variations (e.g., variations in sheet resistance of the material used in heater elements; mask alignment variations, which lead to variations in the width and length of heater elements; the rise and fall times of transistors that drive the heater elements; the thickness of the layer between the heater element and the ink, which influences heat transfer to the ink; the ink chemistry; and the voltage level of the power source), which in turn result in printheads that require differing amounts of energy to attain a drop velocity deemed suitable (e.g., high enough) for attaining a desired print quality. Thus, typically, from printhead to printhead, the amount of energy required to attain a suitable drop velocity varies.
Because of these manufacturing variations, an energy level for driving such printheads will be selected so that most printheads will attain a certain minimum drop velocity (e.g., 400-600 inches per second). This energy level is a statistical average value meant to encompass the largest range of printhead variations possible. Because the same predetermined amount of energy is used for each printhead, the energy is not optimized for a particular printhead.
One problem with this manner of ink delivery is that variations in the printheads lead to inefficiencies in printhead operation. The result is drop velocity variations and difficulty in maintaining nominal head temperatures. Another problem is that driving ink jet heaters at an energy level required to jet ink at an acceptable drop velocity means overdriving some printheads. By overdriving printheads, the overdriven nozzles can fail prematurely due to electromigration of the heater element.
What is needed in the art is a method and apparatus that reduces variations in drop velocities among a type of printhead, and/or provides for fire energy adjustment for the printhead.
The present invention provides, in one embodiment, an apparatus and method for measuring ink drop velocities and adjusting the energy used to eject ink.
The invention, in one form thereof, is directed to a method of adjusting fire energy supplied to an actuator of a printhead of an ink jet printer. The method includes printing a test pattern on a print media by selectively supplying energy distribution signals to a plurality of actuators of the printhead, the energy distribution signals having distinct energy profiles; scanning the test pattern to obtain offset values, each of the offset values representative of a distance between at least two corresponding portions of the test patterns; calculating drop velocities from the offset values; and selecting from the energy distribution signals an energy distribution signal that corresponds with an optimal one of the drop velocities.
The invention, in another form thereof, is directed to an ink jet printer. The ink jet printer includes a controller, a sensor and a printhead having actuators that are capable of jetting ink with a drop velocity when an energy distribution signal having a fire energy is supplied. The controller is capable of communicating with the printhead and the sensor. The controller employs a method including printing a test pattern on a print media by selectively supplying energy distribution signals to a plurality of the actuators of the printhead, the energy distribution signals having distinct energy profiles; scanning the test pattern with the sensor to obtain offset values, each of the offset values representative of a distance between at least two corresponding portions of the test pattern; calculating drop velocities from the offset values; and selecting from the energy distribution signals an energy distribution signal that corresponds with an optimal one of the drop velocities.
The invention, in yet another form thereof, is directed to an imaging device including a carrier, a printhead carrier by the carrier, a sensor carried by the carrier, and a controller communicatively coupled with the printhead and the sensor. The controller is configured to print an image on a sheet of print media. The image includes a test pattern. The controller employs an energy distribution signal adjustment method to determine an energy profile for the printhead.
The aforementioned energy distribution signal adjustment method includes printing the test pattern using distinct energy profiles; scanning the test pattern with the sensor to obtain offset values, wherein a respective one of the offset values is representative of a distance between corresponding portions of the test pattern; and calculating drop velocities corresponding to the distinct energy profiles based on the offset values; Based on the drop velocities, an optimal energy profile is determined. The optimal energy profile is determined by using the drop velocities to determine when an incremental change in energy corresponds with a disproportionate change in drop velocity.
The invention, in yet another form thereof, is directed to a method of optimizing an energy distribution signal for use by a printhead including a plurality of heater elements. The method includes printing a test pattern using energy profiles; scanning the test pattern to obtain offset values, wherein a respective one of the offset values is representative of a distance between corresponding portions of the test pattern; and calculating drop velocities corresponding to the energy profiles, wherein the optimal energy profile is determined by using the drop velocities to determine when an incremental change in energy corresponds with a disproportionate change in drop velocity. An energy distribution signal corresponding to the optimal energy profile is selected.
The invention, in still a further form thereof, is directed to a method of optimizing a relationship between fire energy and drop velocity. In such a method, a test pattern is printed by selectively supplying energy distribution signals to a plurality of actuators of a printhead. The energy distribution signals have distinct energy profiles. The test pattern is scanned to obtain drop velocity information corresponding to the energy distribution signals. Based on the drop velocity information, an energy profile is determined that optimizes the relationship between fire energy and drop velocity.
An advantage of certain embodiments of the present invention is that the fire energy used in an ink jet printer printhead is optimized thereby increasing the life of the printhead.
Another advantage of certain embodiments of the present invention is that the printhead heats less; thus, throughput levels of the printer can increase since the time required to cool a printhead is reduced or eliminated.
Still yet another advantage of certain embodiments of the present invention results from allowing thin film printheads to run open loop without any temperature sensor resistor being required.
A further advantage of certain embodiments of the present invention is that variations that occur in the manufacture of the printhead can be compensated.